Cellulosic fiber products such as paper, paper board, corrugated paper board, hard board, fiber board, gypsum board, chip board, particle board and others have been used for many years in a variety of end uses including the formation of packaging materials and as structural components. The cellulosic fiber products have the advantages of being inexpensive and readily available. However, in certain environments where standing water, aqueous mists, aqueous sprays, or high humidity can be present, the tendency of cellulosic material to readily absorb water can pose a principal disadvantage since wet cellulose can lose strength.
The water absorbed into the cellulosic materials can cause weakness by weakening the cellulosic sheet and by weakening glues that hold the materials together. Many cellulosic fiber products are made by suspending finely divided cellulose particles in aqueous suspensions and forming sheets of the cellulosic materials. This production method can leave the sheets susceptible to the harmful effects of water. Further, the sheets are often combined into structural units using aqueous glues or adhesives in order to insure the cellulosic sheets are solidly bonded. Water, when absorbed by the cellulosic fibers, can be transported to the glue line and can reduce the adhesive bonding strength.
In the past it has been most common to coat or impregnate cellulosic fiber products with hydrophobic materials such as waxes or synthetic resins to impart a degree of water or grease resistance and to improve structural integrity. Waxes, polyolefin resins and mixtures thereof, for example, have been used in the production of films or foils for lamination over substrates such as particle board, which are then used as packaging or structural units. Starches and modified starches have also been used for many years for sizing paper products and for improving water resistant properties of cellulosic fiber products. More particularly, U.S. Pat. No. 347,200 discloses coating cellulosic sheets with a hot melt of paraffin wax and natural resins. McGill, U.S. Pat. No. 2,091,180 teaches the use of a paraffin wax-dihydronaphthalene resin coating for paper products. Miller, U.S. Pat. No. 2,127,650 teaches a melt coating of hexamethylenetetraamine in combination with paraffin, an aluminum salt such as aluminum formate, and gelatin. Hyde, U.S. Pat. No. 2,582,037 teaches forming a coating on paper products having a microcrystalline wax, polyethylene and paraffin wax. Boenau, U.S. Pat. No. 3,105,823 teaches a hot melt coating of polyethylene and wax for paper products. Fordella, U.S. Pat. No. 3,321,428 teaches the use of a hot melt coating including wax and an ethylene unconjugated diolefin copolymer. Moyer, U.S. Pat. No. 3,522,081 teaches a wax coating for paper fibrous products including paraffin wax, an ethylene vinyl acetate polymer, a resin and polyethylene. Gotoh, U.S. Pat. No. 4,117,199 teaches a coating for paper comprising an aqueous emulsion of a rubber latex and a wax emulsion.
The waterproofing materials discussed above are most commonly applied to the cellulosic fiber sheets in the form of continuous films or in another continuous form resulting in water repellancy. Continuous films tend to form a coating which can completely seal the individual cellulosic fibers in the sheet from the environment. Since the sheet is separated from the environment by a substantial film of material, aqueous glues, aqueous dyes, and aqueous inks can be substantially prevented from penetrating such a film and contacting the fibers. The barrier can in this way prevent the successful gluing, coloring, or printing of the coated sheets since the individual fibers cannot interact with the glue, dye or ink.
Aqueous glues, dyes and inks are commonly applied directly to the surface of a cellullosic sheet and act by associating directly with the cellulosic fibers. Most aqueous glues, dyes and inks comprise aqueous solutions or suspensions of at least partially hydrophilic compounds which associate with the hydrophilic cellulosic fibers in order to bond sheet to sheet or to bond dyes or inks to the fibers. In the absence of direct association between these compositions and the cellulosic fiber, successful gluing, dyeing and printing cannot always be obtained.
Further, many waterproofing processes use a melt of wax, rosin, or modified starch which are applied in large amounts to the surface of cellulosic sheets at relatively high temperature. These processes are commonly energy intensive and require substantial amounts of material in order to provide any substantial water resistance.
Accordingly, a substantial need exists for low cost waterproofing composition that can be applied to cellulosic sheets at near ambient temperature which provides water resistance to the sheets and does not prevent the interaction of the cellulosic fibers with aqueous glues, dyes, and printing inks.